1. Field of the Invention
The present invention relates to a film deposition apparatus and a film deposition method for depositing a film on a substrate by carrying out cycles of supplying in turn at least two source gases to the substrate in order to form a layer of a reaction product, and a computer readable storage medium storing a computer program for causing the film deposition apparatus to carry out the film deposition method.
2. Description of the Related Art
As a film deposition technique in a semiconductor fabrication process, there is a technique in which a first reaction gas is adsorbed on a surface of a semiconductor wafer (referred to as a wafer hereinafter) under vacuum and then a second reaction gas is adsorbed on the surface of the wafer in order to form one or more atomic or molecular layers through reaction of the first and the second reaction gases on the surface of the wafer; and such an alternating adsorption of the gases is repeated plural times, thereby depositing a film on the wafer. This technique is referred to, for example, Atomic Layer Deposition (ALD) or Molecular Layer Deposition (MLD). This technique is advantageous in that the film thickness can be controlled at higher accuracy by the number of times alternately supplying the gases, and in that the deposited film can have excellent uniformity over the wafer. Therefore, this deposition method is thought to be promising as a film deposition technique that can address further miniaturization of semiconductor devices.
Such a film deposition method may be preferably used, for example, for depositing a dielectric material to be used as a gate insulator. When silicon dioxide (SiO2) is deposited as the gate insulator, a bis(tertiary-butylamino) silane (BTBAS) gas or the like is used as a first reaction gas (source gas) and ozone gas or the like is used as a second gas (oxidation gas).
In order to carry out such a deposition method, use of a single-wafer deposition apparatus is being considered. The single-wafer deposition apparatus includes a vacuum chamber having a pedestal provided therein and a shower head placed at a top portion of the vacuum chamber facing the pedestal. With such a deposition method using the deposition apparatus, reaction gases are supplied from the shower head to a wafer placed on the pedestal, and unreacted gases and by-products are evacuated from a bottom portion of the chamber. In this case, when plural reaction gases are mixed inside the vacuum chamber, reaction products are generated. This results in the formation of particles. With this deposition apparatus, it is necessary to supply, for example, inert gas as purge gas to replace one reaction gas with another. Replacing of reaction gases takes a long time and the number of cycles may reach several hundred. This results in a problem of an extremely long process time. Therefore, a deposition method and apparatus that enable high throughput is desired.
Under these circumstances, use of an apparatus disclosed in Patent Documents 1-4 is being considered. In schematically describing this apparatus, the apparatus has a vacuum chamber including a pedestal for placing plural wafers arranged in a circumferential direction (rotation direction) and a gas supplying part being placed above the vacuum chamber facing the pedestal for supplying process gas to the wafers. The gas supplying part is arranged, for example, in plural areas in a circumferential direction so that they correspond to the arrangement of wafers on the pedestal.
In order to decompress the inside of the vacuum chamber having wafers placed on the pedestal at a predetermined process pressure, the pedestal and the plural gas supplying parts are relatively rotated around a vertical axis along with heating the wafers and supplying plural kinds of gases (the above-described first and second reaction gases) on the surface of the wafers from each of the gas supplying parts. Further, in order to prevent reaction gases from mixing inside the vacuum chamber, a process area formed by the first process gas and another process area formed by the second process gas are partitioned inside the vacuum chamber by providing physical partition walls between the gas supplying parts or forming a gas curtain with inert gas.
Accordingly, although plural kinds of gases are simultaneously supplied into the same vacuum chamber, because the process areas are partitioned for preventing reaction gases from mixing, the first and second reaction gases, from the standpoint of the rotating wafer, can be alternately supplied via the partition walls or the gas curtain. Therefore, a film deposition process is performed using the above-described method. Accordingly, benefits such as being able to perform film deposition in a short time owing to no need for gas replacement and being able to reduce the consumption amount of inert gas (e.g., purge gas) can be attained.
In introducing plural kinds of reaction gases into the same vacuum chamber, this apparatus not only needs to prevent the reaction gases from mixing with each other in the vacuum chamber but also needs to maintain a constant gas flow with respect to the wafers by strictly controlling the gas flow of the reaction gases in the vacuum chamber. In other words, because this apparatus has plural process areas formed in the vacuum chamber, turbulence of the gas flow to the wafers causes the size of the process areas, that is, the reaction time between the wafer and the reaction gases, to change. This may affect the quality of the thin film formed by the film deposition.
In a case where turbulence of gas flow of reaction gases inside the vacuum containers is caused in an in-plane part or a space between the surfaces of the wafers (e.g., a case where a necessary amount of reaction gas is not supplied to the wafers), there is a risk of the film thickness becoming reduced due to insufficient attraction of the reaction gases or degrading of film quality due to, for example, insufficient progress of an oxidation reaction. Further, in a case where reaction gases are mixed via the partition walls or the gas curtain due to turbulence of gas flow, reaction products are generated. The generation of the reaction products causes the formation of particles. Thus, although it is necessary to strictly control the gas flow of the reaction gases, the above-described partition walls or gas curtain is insufficient. Further, even in a case where there is a turbulence of gas flow during processing, such turbulence cannot be recognized.
Furthermore, because this apparatus processes the wafers while maintaining the inside of the vacuum chamber at a predetermined degree of vacuum (pressure), it is necessary to control both the degree of vacuum inside the vacuum chamber and the gas flow of the reaction gases in the vacuum chamber. Therefore, control of the gas flow is extremely difficult. Furthers because the degree of vacuum inside the vacuum chamber or the flow rate of the reaction gases changes according to the recipe of the process performed on the wafers, it is necessary to control the degree of vacuum or the gas flow of the reaction gases with respect to each recipe. This further makes the control difficult. Nevertheless, no consideration is made regarding the control of the gas flow in the above-described Patent Documents.
Patent Document 5 discloses a method of separating a vacuum chamber into a left-side area and a right-side area, forming a gas supply opening and an evacuation opening in each of the areas, supplying different gases in each of the areas, and evacuating gases from each of the areas. However, there is no mention regarding the gas flow inside the vacuum chamber, that is, regarding the flow rate of, for example, the gas evacuated from each evacuation opening. Therefore, even in a case where evacuation flow rate changes with time (e.g., due to accumulation of particles in the evacuation passage) and results in a loss of balance of the evacuation flow rate between the left and right areas (one side evacuation), such loss of balance cannot be recognized. Further, in a case where an evacuation pump is provided to each of plural evacuation channels, a difference of evacuation performance among the evacuation pumps may occur depending on the status of each evacuation pump. However, there is no mention in Patent Document 5 regarding such difference.
Furthermore, Patent Documents 6 through 8 disclose a film deposition apparatus preferably used for an Atomic Layer CVD method that causes plural gases to be alternately adsorbed on a target (a wafer). In this apparatus, a susceptor that holds the wafer is rotated, while source gases and purge gases are supplied to the susceptor from above. In this apparatus, a gas curtain is formed by inert gas, and the source gases and purge gases are separately evacuated from evacuation channels 30a and 30b. However, as with the Patent Document 5, there is no mention regarding the flow rate of the gas evacuated from each of the evacuation channels 30a, 30b. 
Furthermore, there is known a method of providing an evacuation channel with a valve that can have its opening adjusted and estimating the flow rate of evacuation gas flowing in an evacuation channel from the opening of the valve. This method, however, does not measure the actual flow rate of evacuation gas. Therefore, the actual flow rate of evacuation cannot be recognized in a case where, for example, there is a change in the evacuation performance of the evacuation pump as described above.
Patent Document 1: U.S. Pat. No. 6,634,314
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2001-254181 (FIGS. 1, 2)
Patent Document 3: Japanese Patent Publication No. 3,144,664 (FIGS. 1, 2, claim 1)
Patent Document 4: Japanese Patent Application Laid-Open Publication No. H4-287912
Patent Document 5: U.S. Pat. No. 7,153,542 (FIGS. 6A, 6B)
Patent Document 6: Japanese Patent Application Laid-Open Publication No. 2007-247066 (paragraphs 0023 through 0025, 0058, FIGS. 12 and 18)
Patent Document 7: United States Patent Publication No. 2007-218701
Patent Document 8: United States Patent Publication No. 2007-218702